1. Field of the Invention
The present invention relates to a receiver for regenerating a signal wave from a received wave, and in particular to a receiver for regenerating a signal wave via digital signal processing.
2. Related Art
Conventionally, an analog receiver of the superheterodyne system is known as a receiver for receiving a broadcast wave transmitted from a broadcast station and regenerating a signal wave in the audio frequency band.
The analog receiver converts a broadcast wave to an IF signal of the intermediate frequency and removes unwanted frequency components by passing the IF signal through a band-pass filter 1 the intermediate frequency band as shown in FIG. 14, and obtains a signal wave (detection output) via a detection circuit 2.
[Problems to be Solved]
The inventor of the application has formed the aforementioned analog receiver via digital circuits to make an attempt to develop a digital receiver that is compatible with for example digital audio apparatus.
As one of such attempts, the inventor of the application has proposed that the band-pass filter shown in FIG. 14 includes a direct-type secondary IIR (infinite Impulse response) filter 1′ shown in FIG. 15 and that a detection circuit subordinate to the digital band-pass filter 1′ be digitized. That is, the inventor has proposed that the digital band-pass filter 1′ includes digital adders 4, 5, 6, 7, digital delay elements 8, 9, and digital multipliers 10, 11, 12, 13, 14, and that digital data generated by converting an IF signal from a frequency converter undergo digital filtering.
While an IF signal is down-converted by a frequency converter, it is a signal prior to detection. Thus, using an IIR filter of a general configuration in FIG. 15 requires use of a large-scale digital circuit that allows high-speed arithmetic operation, making application to a receiver difficult.